1. Field of the Invention
The present invention relates to input keyboards and, more particularly, to keyboards having a matrix without interconnecting diodes.
2. Description of the Prior Art
Electronic equipment is controlled in a great many cases via an input keyboard which, as a rule, consists of push-button switches arranged in rows and columns. Such electronic equipment may include, for example, electronic computers, electronic pocket calculators, or remote control units for e.g. phono equipment, radio or television receivers. The pushbutton switches, while being actuated, serve to establish electrical connections between input leads which may be associated with the aforementioned rows and columns. Thus, in the "IBM Technical Disclosure Bulletin", October 1966, on pages 532/33 there is described a keyboard circuit for data-processing systems in which the information is offered via the just depressed pushbutton switch in a three-out-of eight code. The pushbutton switches as such, are simple two-pole switches acting as operating contacts. Each pushbutton switch is associated with four decoupling diodes connecting it with four of nine input leads of the data-processing system which, in turn, continuously interrogates the input keyboard with the aid of sampling signals, thus detecting a depressed pushbutton switch. Accordingly, this is a dynamically operating arrangement.
On page 36 of the technical journal "Electronic Engineering" for September 1976, there is described another data-processing system whose input keyboard cooperates with the integrated circuit of the type MC 14419 which is described in greater detail on pages 5/201 to 5/204 of the data book published by the firm of Motorola "Semiconductor Data Library", Vol. 5, Series B, 1976. From FIG. 4 as shown therein, it is to be seen that the pushbutton switches must be either equipped with double contacts because they, when actuated, apply a supply voltage to the respective column or row lead, or that a pushbutton switch with a single contact may be provided for when being connected to the respective column or row lead via two diodes. It is obvious that such a design or such a wiring of the pushbutton switches is more expensive than the pushbutton switches employing a single contact proposed for use by the aforementioned passage of literature. The aforementioned integrated circuit of the type MC 14419 contains a two-out-of-eight encoder with a subsequently arranged code converter for obtaining a binary-coded decimal (BCD). This circuit likewise operates dynamically, i.e. there is provided a clock oscillator for controlling the code-forming sequence.
From a further data sheet published by the firm of Motorola Semiconductors, No. E 175, June 1976, it is known to use the integrated circuit of the type MC 14422 P as realized in accordance with the known CMOS-technique, with remote control transmitters, which likewise operates dynamically and, for this purpose contains a sampling oscillator, a sampling control circuit and further additional circuits. In this arrangement, it is likewise possible to use single-pole pushbutton switches. Finally, from the technical journal "Electronics", of Jan. 6, 1977, pp. 110 to 112 there is known an input keyboard employing simple pushbutton switches in which the respective depressed key is ascertained with the aid of the microprocessor F8, for which the corresponding program (software) is disclosed in the publication.
Accordingly, the two last-mentioned publications show arrangements solving the keyboard coding problem with an investment which is relatively high also with respect to integrated circuits. In particular, the last-mentioned publication including the proposal of using for this purpose a commercially available type of microprocessor, is not realizable in cases where, for example with the aforementioned remote control units, the keyboard coding as well as the remaining remote control transmitter circuit is to be accommodated in one single integrated circuit. In such a case, the keyboard coding arrangement must do with as little as possible crystal surface in order to leave enough crystal surface of the integrated circuit for being utilized for the actual functioning of the remote control transmitter. When looked at from this point of view, it would appear to be entirely mistaken to provide a microprocessor, because substantial parts thereof would remain unused. But also the aforementioned dynamic technique is too expensive for meeting the given requirement.